Run the scripts asynchronously

[gflegar]

For large datasets, running the JSONata script can take a while. Currently, this is done in the UI thread, which means that the application is frozen until the script is executed. To alleviate the issues, the scripts should be run in a separate thread by using web workers (this tutorial may be useful for angular).

And we may want to add some progress bars to the UI to tell the user when the scripts are running.